This is a three-period crossover phase I study designed to evaluate the relative bioavailability, food effect, safety and tolerability of SYHA1813 oral solution in healthy participants.

Avoid duplicating information that will be entered elsewhere, such as Eligibility Criteria or Outcome Measures.

Inclusion Criteria:

1. Healthy male aged 18 to 60 years old;
2. Weight more than 50.0 kg and body mass index between 19 to 26.0 kg/m^2;
3. Normal or abnormal results without clinical significance on all tests including medical history, vital signs, physical examination, laboratory evaluation (routine blood, blood biochemistry, urine routine, coagulation function, serum virology, and other related tests), 12-lead electrocardiogram, chest X-ray and other tests;
4. Male participants and their partners must agree to use effective non-hormonal contraception from the first administration of the test drug to 6 months after the last administration of the test drug, even if permanent contraception has already been used, and the male participant does not plan to donate sperm;
5. Voluntarily sign the informed consent form, and cooperate in completing the trial according to the protocol.

Exclusion Criteria:

1. Allergic constitution (allergic to 2 or more kinds of drugs, food, or pollen);
2. Participants with a clear history of neurological disease or psychiatric disease, a history of severe cardiovascular, hepatic, renal, endocrine, respiratory, hematologic, digestive, immune, and other various systemic diseases, or a history of malignant neoplastic disease;
3. Participants who are unable to swallow orally administered drugs, or clinically significant abnormalities in gastrointestinal function that could affect drug absorption, distribution, metabolism, and excretion;
4. Participants who have undergone major surgery within 6 months prior to screening or who are scheduled to undergo surgery during the trial;
5. Participants with 1 or more abnormal vital signs at screening;
6. Abnormal and clinically significant electrocardiograms: QTc interval >450ms;
7. Participants who consumed more than 14 units of alcohol per week in the 4 weeks prior to screening or who had a positive breath test for alcohol at screening;
8. Smoking ≥ 5 cigarettes per day on average within 6 months prior to screening;
9. Participants with a history of drug or substance abuse, or a positive urine drug screen;
10. Participants who have lost blood or donated more than 400 ml of blood within 4 weeks prior to screening or plan to donate blood during the study or within 1 month of the end of the study;
11. Participants who have participated in other clinical trials within 3 months prior to screening;
12. Habitual intake of excessive xanthine or caffeine-containing foods, beverages, or other foods that interfere with drug absorption, distribution, metabolism, excretion within 4 weeks prior to screening;
13. Participants who have taken a special diet (dragon fruit, mango, grapefruit, lime, poppy seed, or food or drink prepared from them) within 7 days prior to screening, or participants who are unable to stop taking the above special diets during the trial;
14. Participants who have used potent inhibitors or inducers of CYP enzymes (e.g., CYP2C9, 2C19, and 3A4) within 4 weeks prior to screening;
15. Participants who have used prescription, over-the-counter, herbal, vitamin, or mineral medications within 2 weeks prior to screening, and participants who have taken medications prior to screening that have not completed 5 half-lives, whichever is longer among the various medications;
16. Participants who cannot tolerate venipuncture or with a history of fainting needle or blood;
17. Participants who are lactose intolerant;
18. Any condition that the investigator considers inappropriate for participation in the study.